Survey-augmented navigation system for an aircraft

ABSTRACT

A system having components coupled to an aircraft and components remote from the aircraft processes radar-augmented data, transmits information between aircraft system components and/or remote system components, and dynamically determines locations and states of the aircraft, while the aircraft is in flight. Based on the locations and states of the aircraft, the system generates instructions for flight control of the aircraft toward a flight path appropriate to the locations of the aircraft, and can update flight control instructions as new data is received and processed.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/157,968, filed Oct. 11, 2018, which is incorporated by referenceherein.

BACKGROUND

This disclosure relates generally to navigation systems, and morespecifically to systems and methods for performing survey-augmentednavigation during flight of an aircraft.

Proper navigation of an aircraft during flight is critical in relationto ensuring correct operation of an aircraft according to airspace type,according to terrain limitations, and/or according to differentenvironmental situations. Successful navigation requires that theposition, orientation, and motion states of an aircraft be known to ahigh degree of certainty at all times during flight of the aircraft.Current systems for automated navigation onboard an aircraft and/orremote from the aircraft require installation and maintenance ofexpensive apparatus, lack a high degree of precision, are not reliableto a high enough degree, drift in accuracy, and/or are prone tointerference. The inventions described herein relate to improved systemsand methods navigation, and can be used for automated control of anaircraft during flight.

SUMMARY

While an aircraft is in flight, a system having components coupled tothe aircraft and components remote from the aircraft processessurvey-augmented data (e.g., radar-augmented data), transmitsinformation between aircraft system components and/or remote systemcomponents, and dynamically determines locations and states of theaircraft. The system and methods implemented by the system fusesinformation from a non-traditional navigation system architecture toprecisely determine locations of the aircraft during flight. The systemarchitecture also corrects for drift in accuracy of navigationsubsystems and/or allows navigation subsystems to operate continuouslywhen one or more subsystems of the navigation subsystems areunavailable. Based on the locations and states of the aircraft, thesystem can also generate instructions for flight control of the aircrafttoward a flight path appropriate to the locations of the aircraft, andcan update flight control instructions as new data is received andprocessed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic of a system for navigation, in accordance withone or more embodiments.

FIG. 1B is a schematic of operation modes of a system for navigation, inaccordance with one or more embodiments.

FIG. 2A depicts a flowchart of a method for navigation, in accordancewith one or more embodiments.

FIG. 2B depicts a schematic of a method flow according to embodimentsshown in FIG. 2A.

FIG. 2C depicts a schematic of navigation based on terrain featuredetection, in accordance with one or more embodiments.

FIG. 3A depicts a schematic of a portion of the method shown in FIGS.2A-2B.

FIG. 3B depicts a schematic of another portion of the method shown inFIGS. 2A-2B.

FIG. 4A depicts a schematic of navigation based on static objectdetection, in accordance with one or more embodiments.

FIG. 4B depicts a schematic of navigation based on activatable markerdetection, in accordance with one or more embodiments.

FIG. 4C depicts a schematic of navigation based on moving objectdetection, in accordance with one or more embodiments.

The figures depict various embodiments for purposes of illustrationonly. One skilled in the art will readily recognize from the followingdiscussion that alternative embodiments of the structures and methodsillustrated herein may be employed without departing from the principlesdescribed herein.

DETAILED DESCRIPTION 1. System for Survey-Augmented Navigation

FIG. 1A depicts a schematic of a system 100 for navigation, inaccordance with one or more embodiments. The system 100 includes one ormore navigation-related subsystems 110 coupled to (e.g., mounted to,onboard, within, etc.) an aircraft 105, where the navigation-relatedsubsystems are described in more detail below. The system 100 can alsooptionally include a remote station 120 in communication with a datacenter 130 at a location remote from the aircraft 105, such that somecomputing functions can be performed at a location remote from theaircraft 105. The system 100 can also include a flight management system(FMS) 150 including interfaces between the remote station 120 to the FMS150 and/or interfaces between the navigation-related subsystems 110 andthe FMS 150. The system 100 provides structures, subsystem interfaces,and operation modes useful for performing automated flight operations,including operations associated with methods described in more detail inSection 2 below.

The system 100 functions to augment low altitude flight operations, suchas operations below a threshold altitude, with data from supplementalnavigation subsystems, in order to generate better estimates of statesof the aircraft in terms of position, movement, and orientation.Generation of more accurate estimates of aircraft state, especially inlow altitude conditions, can improve navigation-based decision making(e.g., automated decision making) and flight planning for the aircraft105. The system uses specialized radar tools to determine candidatelocations of an aircraft during flight, and augments data from othernavigation subsystems to hone in on a more precise location of theaircraft to assist navigation operations. The system also corrects fordrift in accuracy of navigation subsystems and/or allows navigationsubsystems to operate continuously when one or more subsystems of thenavigation subsystems are unavailable.

1.1 System—Aircraft

The aircraft 105 shown in FIG. 1 is a fixed-wing aircraft. The aircrafthas flight control surfaces for aerodynamically affecting flight of theaircraft relative to a pitch axis (i.e., a transverse axis), a yaw axis(i.e., a vertical axis), and a roll axis (i.e., longitudinal axis) ofthe aircraft. Flight control surfaces can include one or more of:ailerons, flaps, elevators, stabilizers (e.g., horizontal stabilizers),rudders, spoilers, slats, air brakes, vortex generators, trim surfaces,and any other suitable control surfaces. The aircraft also has a powerplant for generation of mechanical power associated with flightoperations, and in variations, the power plant can include one or moreof: a piston engine (e.g., in-line engine, V-type engine, opposedengine, radial engine, etc.), a gas turbine engine (e.g., turbojetengine, turbofan engine), a pulse jet, a rocket, a Wankel engine, aDiesel engine, an electric engine, a hybrid engine, and any othersuitable power plant system. The power plant is coupled to an energysource (e.g., fuel system, battery, solar cell, etc.) and a coolingsystem (e.g., forced convection cooling system, liquid cooling system,oil cooling system, etc.) for aircraft performance in flight.

While this description uses a fixed-wing aircraft as an example, theprinciples described herein are equally applicable to variations of theaircraft 105 including form factors and/or control surfaces associatedwith one or more of: rotorcraft, gliders, lighter-than-air aircraft(e.g., airships, balloons), powered-lift aircraft, powered-parachuteaircraft, weight-shift-control aircraft, rockets, vertical takeoff andlanding (VTOL) aircraft (e.g., electric VTOL aircraft), and/or any othersuitable types of aircraft. Still other variations of the system 100 caninvolve terrestrial vehicles, water vehicles, amphibious vehicles, orother non-aircraft vehicles.

1.2 System—Navigation-related Subsystems

The navigation-related subsystems 110 include subsystems capable ofgenerating data associated with dynamic states of the aircraft andoperational states and configurations of the aircraft, where thenavigation-related subsystem components 110 produce data that can beprocessed to determine locations of the aircraft during flight. Thenavigation-related subsystems 110 also include subsystems capable oftransmitting data from the aircraft 105 and other remote systems.

The navigation-related subsystems 110 include subsystems that generateand receive information generated from subsystems coupled to theaircraft 105, as well as a flight computer 116 providing computationalinfrastructure (e.g., processing components, communication buses,memory, storage etc.) for communicating data between the subsystems. Theflight computer 116 thus provides architecture for communication of datagenerated by subsystems, for communication with other systems remotefrom the aircraft 105, for control of subsystems, and/or for control ofthe aircraft. The flight computer 116 can also include architecture forreporting navigation-associated information to an operator (e.g., pilot)of the aircraft 105, for instance, in manual operation modes orsemi-manual operation modes where navigation states can be displayed tothe operator (e.g., through an electronic flight instrument system). Thenavigation-related subsystems 110 can thus include specialized computercomponents designed for use in an aircraft, and in particular, caninclude components that are customized in configuration relative to eachother and customized in relation to processing of signals received andprocessed to perform aspects of the methods described in Section 2below.

Information routed between subsystems of the navigation-relatedsubsystems 110 can optionally be routed through a flight managementsystem (FMS) 150 that is configured for automation of flight tasks inrelation to a flight plan. The FMS 150 processes navigation databaseinformation (e.g., information associated with waypoints, airways,navigation aids, airports, runways, departure procedures, arrivalprocedures, holding patterns, etc.), aircraft subsystem statuses, andoutputs of other subsystems and determines one or more desired flightpaths based on the information. The FMS 150 can cooperate with theflight computer 115 in receiving outputs of other subsystems of thenavigation-related subsystems 110 and/or transmitting controlinstructions to affect operational states of other subsystems of thenavigation-related subsystems 110. The FMS 150 can also include orinterface with other control systems (e.g., of an autopilot) totransform calculated flight information into instructions for control ofcontrol surfaces of the aircraft 105 including one or more of: ailerons,flaps, elevators, stabilizers (e.g., horizontal stabilizers), rudders,spoilers, slats, air brakes, vortex generators, trim surfaces, and anyother suitable control surfaces.

1.2.1 System—Navigation-related Subsystems—Radar Subsystem

As shown in FIG. 1A, the navigation-related subsystems 110 include aradar subsystem 111 mounted to the aircraft, where the radar subsystem111 includes radar transmit and receive antennas configured to enabledetection of features of objects associated with a flight path of theaircraft. Radar transmit antennas of the radar subsystem 111 emit in theradio portion of the electromagnetic spectrum. Radar transmit antennascan further transmit signals that have a wavelength, gain, carrier,pulse width, pulse repetition frequency, staggering, and any othersuitable characteristic suitable for generation of return signals thatcan be processed to determine features of objects interacting with thetransmitted signals. Radar receive antennas of the radar subsystem 111receive in the radio portion of the electromagnetic spectrum and receivesignals that have an effective aperture and gain. Radar receive antennascan be coupled with elements (e.g., filters, polarizers, etc.)configured to prevent or otherwise mitigate undesired return signalsassociated with clutter, interference, noise, and/or jamming. Radarreceive antennas can additionally or alternatively be coupled withelements (e.g., attenuators) configured to prevent saturation of thereceive elements from a return signal. Radar transmit and/or receivecomponents can, however, be coupled to any other suitable elements(e.g., waveguides, duplexers, etc.) that refine aspects of the emittedand/or received signals in a desired manner. Furthermore, radar antennascan include phased array configurations (e.g., passive phased arrayconfigurations, active phased array configurations, conformal phasedarray configurations, etc.) or other suitable antenna configurations.

The radar subsystem 111 can have one or more radar antennas structurallymounted to the aircraft and positioned so as to transmit signals awayfrom a ventral surface of the aircraft 105 and/or receive signalstransmitted or reflected toward the ventral surface of the aircraft. Assuch, radar antennas can be configured to receive signals from terrainand/or other objects below the aircraft during flight. Antennas of theradar subsystem 111 can alternatively be positioned relative to theaircraft in any other suitable manner (e.g., coupled to a non-ventralsurface) in order to receive signals that can be processed to determinelocations of the aircraft in flight.

Multiple radar antennas can be used for system redundancy (e.g., in theevent a subset of antennas are compromised). Multiple radar antennas canalso be used for providing different positions from which to emit radarsignals toward objects of interest and/or for receiving radar signalsfrom objects of interest, depending upon orientation of the aircraft 105or characteristics of objects from which return signals are generated.

The antenna(s) of the radar subsystem 111 can be coupled to an exteriorportion of the aircraft 105. One or more antenna(s) of the radarsubsystem 111 can alternatively be coupled to an interior portion of theaircraft 105 and extend through a wall of the aircraft 105 to transmitand/or receive signals outside of the aircraft 105. Mounting positionsare associated with desired directionality in relation to transmittedradar signals and/or received signals, in relation to relativeorientations between the aircraft and objects used to determine thelocation(s) of the aircraft 105 during flight. The antenna(s) of theradar subsystem 111 can thus be fixed in position. The antenna(s) of theradar subsystem 111 can alternatively be adjustable in position and/orrotation based on orientations of the aircraft in flight. The radarsubsystem 111 can thus include actuators coupled to the antenna(s) ofthe antenna subsystem 111 and/or position encoders coupled to theactuators, in relation to electronic control of antenna positions.

The radar subsystem 111 produces output signals that have acharacteristic resolution and power, and from which transmittime-related parameters (e.g., time between transmission of a signal andreceipt of a return signal), distance-related parameters (e.g., distancebetween the aircraft and an object), reflector object parameters (e.g.,shape, surface features, etc.), scattering parameters, frequencymodulation parameters, speed-related parameters (e.g., change indistance between the aircraft and an object), and/or any other suitableparameters can be extracted to determine a location of the aircraftduring flight.

Furthermore, while images are described, the radar subsystem 111 can besupplemented with or otherwise replaced with a light detection andranging (LIDAR) subsystem that includes light emission elements and/orlight sensors for receipt of optical signals indicative of featuresabout the aircraft (e.g., in relation to light reflective objects, lightscattering objects, light absorbing objects, light responsive objects,etc.), where the optical signals can be processed to determine locationsof the aircraft 105 during flight, in relation to the method(s)described in Section 2 below. In still other variations, the radarsubsystem 111 can be supplemented with or otherwise replaced with othercamera components (e.g., stereo cameras, monocular cameras) thatgenerate information (e.g., stereo information from which heightinformation can be derived) while the aircraft 105 is in motion, wherethe height information can be used to determine locations of theaircraft 105 during flight, in relation to the method(s) described inSection 2 below. As such, the system 100 can implement other sensorsthat provide height information related to positions of the aircraft105, in order to augment navigation of the aircraft 105 in space.

1.2.2 System—Navigation-Related Subsystems—IMU Components

The navigation-related subsystems 110 also include one or more inertialmeasurement units (IMUs) 112 for measuring and outputting dataassociated with the aircraft's specific force, angular rate, magneticfield surrounding the aircraft 105, and/or other position, velocity, andacceleration-associated data. Outputs of the IMU(s) can be processedwith outputs of other aircraft subsystem outputs to determine poses ofthe aircraft 105 relative to a landing site (or other target), and/orpose trajectories of the aircraft 105 relative to a landing site (orother target). The IMU 112 includes one or more accelerometers, one ormore gyroscopes, and can include one or more magnetometers, where any orall of the accelerometer(s), gyroscope(s), and magnetometer(s) can beassociated with a pitch axis, a yaw axis, and a roll axis of theaircraft 105.

The IMUs 112 are coupled to the aircraft, and can be positioned internalto the aircraft or mounted to an exterior portion of the aircraft. Inrelation to measurement facilitation and/or post-processing of data formthe IMU, the IMU can be coupled to a vibration dampener for mitigationof data artifacts from sources of vibration (e.g., engine vibration) orother undesired signal components.

1.2.3 System—Navigation-related Subsystems—GPS Components

The navigation-related subsystems 110 can include a global positioningsystem (GPS) 113 coupled to the aircraft and including antennas tuned tofrequencies transmitted by satellites for receiving location-associatedand velocity-associated data of the aircraft 105. The GPS 113 has a GPSprocessor, a clock, and a data link (e.g., wireless data link, wireddata link). The GPS 113 can include a display, and can include anysuitable number of channels (e.g., greater than 12 channels, less thanor equal to 12 channels, etc.) for monitoring of different satellites.The GPS 113 can be electronically coupled to an electrical system of theaircraft 105 for power and/or alternatively include an independent powersource (e.g., for a portable configuration). The GPS 113 can further becoupled to other subsystems of the navigation-related subsystems 111.The GPS 113 can additionally or alternatively be coupled to the FMS 150.The GPS 113 can include one or more receiver inputs for differentialcorrections (e.g., using an RTCM SC-104 format) and/or can be configuredas a wide area augmentation system (WAAS) receiver. Furthermore, the GPS113 can include architecture for relaying data (e.g.,location-associated data, time-associated data, velocity-associateddata, etc.) to other data processing devices using a NMEA 0183 protocolor any other suitable protocol (e.g., SiRF protocol, MTK protocol,etc.).

The GPS 113 can have one or more receivers coupled to the aircraft 113(e.g., within the aircraft, mounted to the aircraft) and positioned soas to mitigate interference from other portions of the aircraft 105(e.g., structural features of the aircraft) and/or other subsystemsassociated with the aircraft 105.

In relation to the IMU 112, the GPS 113 can also be communicativelycoupled to the IMU 112 as an IMU-enabled GPS. In IMU-enabled GPSconfigurations, the GPS 113 can thus include operation modes that outputlocation-associated information and/or velocity-associated informationwhen satellite signals to the GPS 113 are unavailable, based on positionand velocity outputs of the IMU 112 and a reference location of theaircraft 105 from the GPS, when satellite signals to the GPS 113 wereavailable.

In relation to the GPS 113, the navigation-related subsystems 110 canalso include a satellite transmission subsystem 114 including relays forinterfacing with one or more satellites including satellite 14. Thesatellite transmission subsystem 114 can thus include channelsassociated with the GPS 113 described above in relation to receipt andtransmission of satellite signals associated with the GPS 113. Thesatellite transmission subsystem 114 can additionally or alternativelyinclude channels associated with transmission and/or reception ofsatellite data for traffic avoidance in coordination with automaticdependent surveillance broadcast (ADS-B) functionality, for weatherservices (e.g., in relation to weather along flight path, in relation towinds aloft, in relation to wind on the ground, etc.), for flightinformation (e.g., associated with flight restrictions, for notices,etc.), and/or for any other suitable purpose. The satellite transmissionsubsystem 114 operates in approved frequency bands (e.g., bands approvedthrough Federal Communications Commission regulations, bands approvedthrough Federal Communications Commission advisory circulars, etc.). Thesystem 100 can additionally or alternatively implement other groundand/or space-based augmentation systems.

1.2.4 System—Navigation-related Subsystems—Communication Components

The navigation-related subsystems 110 also include a radio transmissionsubsystem 115 for communication with the aircraft 105, for transmissionof aircraft identification information, or for transmission of othersignals. The radio transmission subsystem 115 can include one or moremultidirectional radios (e.g., bi-directional radios) onboard theaircraft, with antennas mounted to the aircraft in a manner that reducessignal transmission interference (e.g., through other structures of theaircraft). The radios of the radio transmission subsystem 115 operate inapproved frequency bands (e.g., bands approved through FederalCommunications

Commission regulations, bands approved through Federal CommunicationsCommission advisory circulars, etc.).

The communication-related components of the flight data subsystems 110can additionally or alternatively cooperate with or supplement data fromother avionics components (e.g., the GPS 113), electrical components(e.g., lights), and/or sensors that support flight operations (e.g., inflight, during landing, on the ground, etc.), that support observabilityby other traffic, that support observability by other aircraft detectionsystems, that provide environmental information (e.g., pressureinformation, moisture information, visibility information, etc.) and/orperform other functions related to aircraft communications andobservability.

Furthermore, the system 100 can operate in multiple modes. For instance,in a first operation mode, the system 100 can implement onboardradar-augmented (or other height data-augmented) navigation systemcomponents to locally make navigation decisions for the aircraft 105. Ina second operation mode, the system 100 can implement remoteradar-augmented (or other height data-augmented) navigation systemcomponents to remotely make navigation decisions for the aircraft 105.

1.3 System—Remote Components

As shown in FIG. 1A, the system 100 can optionally include a remotestation 120 that includes devices for wirelessly receiving data from andtransmitting data to subsystems coupled to (e.g., onboard, theaircraft). The remote station 120 includes one or more multidirectionalradios (e.g., bi-directional radios) onboard the aircraft, with antennasmounted to the aircraft in a manner that reduces signal transmissioninterference (e.g., through other structures of the aircraft). Theradios of the remote station operate in approved frequency bands (e.g.,bands approved through Federal Communications Commission regulations,bands approved through Federal Communications Commission advisorycirculars, etc.). The remote station 120 is in communication with a datacenter 130 for storage and retrieval of data derived from subsystems ofthe aircraft 105. The data center uses storage and retrieval protocolsand can use data encryption protocols for promoting security in relationto handling sensitive information pertaining to autonomous flight of theaircraft 105.

The remote station 120 can also use communications technologies and/orprotocols in relation to data transmission operations with the datacenter 130, subsystems of the aircraft 105, and/or the operatorinterface 140 described in more detail below. For example, the remotestation 120 can have communication links using technologies such asEthernet, 802.11, worldwide interoperability for microwave access(WiMAX), 3G, 4G, code division multiple access (CDMA), digitalsubscriber line (DSL), or other communication technologies. Examples ofnetworking protocols used for communications with the remote station 120include universal datagram protocol (UDP) and/or any other suitableprotocol. Data exchanged with the remote station 120 can be representedusing any suitable format.

1.4 System—Altitude-based Operation Modes

FIG. 1B depicts a schematic of operation modes of the system 100 shownin FIG. 1A, in accordance with one or more embodiments. As shown in FIG.1B, the system 100 can transition between a first operation mode 100 aassociated with operations at or above a threshold altitude (e.g., aboveground level altitude, mean sea level altitude, etc.) and a secondoperation mode 100 b associated with operations at or below a thresholdaltitude relative to a reference point (e.g., relative to above groundlevel altitude, relative to mean sea level altitude, etc.). In the firstoperation mode 100 a (shown in FIG. 1B, top), the aircraft 105 is abovethe threshold altitude (e.g., 2000 ft. above ground level), and thenavigation-related subsystems 110 include the IMU 112 and the GPS 113 inactive modes and receive functions of the radar subsystem 111 in aninactive mode. In the first operation mode 100 a, the flight computer116 and/or the remote station 120 generate estimates of the state (e.g.,position, orientation, velocity, etc.) of the aircraft 105 uponprocessing outputs of the IMU 112 and the GPS 113 (if satellite signalsto the GPS 113 are available).

In the second operation mode 100 b (shown in FIG. 1B, bottom), theaircraft 105 is at or below the threshold altitude (e.g., 2000 ft. aboveground level), and the navigation-related subsystems 110 include the IMU112 and the GPS 113 in active modes, and receive functions of the radarsubsystem 111 in an active mode. In the second operation mode 100 b, theflight computer 116 and/or the remote station 120 generate estimates ofthe state (e.g., position, orientation, velocity, etc.) of the aircraft105 upon processing outputs of the radar subsystem 111, the IMU 112, andthe GPS 113 (if satellite signals to the GPS 113 are available).

Detection of altitudes of the aircraft relative to the thresholdaltitudes can be implemented by the system 100 based on measurementsoutput from an altimeter of the aircraft 105. Based on detectedaltitudes, the flight computer 116 of the aircraft 105 can transitionsubsystems of the navigation-related subsystems 110 between active andinactive modes according to operation modes 100 a and 100 b.

In alternative embodiments, the radar subsystem 111 may not betransitioned to a fully inactive state in response to altitude of theaircraft 105 or other factors. For instance, the radar subsystem may beperiodically activated above a threshold altitude or in response toanother triggering factor (e.g., to periodically test the system 100).

Still alternatively, transitioning the radar subsystem 111 to aninactive state may be implemented in relation to power limitations(e.g., to conserve energy) in certain aircraft operation modes or due tolocation-based limitations (e.g., in regions or airspaces that requiredeactivation of the radar subsystem 111).

Methods for processing outputs to determine state estimates aredescribed in more detail in Section 2 below.

1.5 System—Conclusion

Variations of elements of the system 100 described above and shown inFIGS. 1A and 1B can be configured in any other suitable manner. Forinstance, portions of one or more of: the flight computer 115 onboardthe aircraft 105, the FMS 150, the remote station 120, and/or the datacenter 130 can operate as a computing system that includesmachine-readable instructions in non-transitory media for implementationof an embodiment of the method 200 described below, in relation to oneor more of: monitoring an altitude status of an aircraft in flight; inresponse to the altitude status satisfying a threshold altitudecondition, transitioning a radar subsystem of the aircraft to a receivemode; from the radar system in the receive mode, characterizing anobject height of an object below the aircraft; generating a set ofcandidate locations of the aircraft from the object height; determininga location of the aircraft upon processing the set of candidatelocations with an inertial measurement unit (IMU) output of an IMUcoupled to the aircraft; updating a state estimate of the aircraft withthe location; generating a set of instructions for flight control of theaircraft toward a flight path appropriate for the location (e.g., withthe FMS 150, etc.); and performing any other method portion described.In relation to flight control, the system 100 can include an electronicinterface between the computing system (e.g., flight computer 116,remote station 120) and an FMS 150 of the aircraft (e.g., as supportedby the computing system), the electronic interface operable in a modethat transmits the set of instructions to the flight management systemand controls flight of the aircraft toward the flight path. One or moreportions of the computing system described above can further includearchitecture for storing a database of navigation object characteristicsrelevant to flight paths of the aircraft 105, where the database ofnavigation object characteristics can include a high-resolution heightmap database of terrain, static objects, infrastructure associated withmoving objects, activatable markers, and/or other features below or inthe path of the aircraft 105 during flight. The database can be accessedby portions of the computing system to facilitate portions of the method200 described below.

Additional aspects of the method 200 are described in further detail inSection 2 below. Further, while the system(s) described above canimplement embodiments, variations, and/or examples of the method(s) 200described below, the system(s) can additionally or alternativelyimplement any other suitable method(s).

2. Method for Survey-Augmented Navigation

FIG. 2A depicts a flowchart of a method 200 for radar-augmentednavigation, in accordance with one or more embodiments. FIG. 2B depictsa schematics of a method flow according to embodiments shown in FIG. 2A.The method 200 functions to process sensor-derived data, transmitinformation between navigation-related subsystems and/or systems remotefrom the aircraft, and dynamically determine estimates of the state(e.g., position, orientation, velocity, etc.) of the aircraft duringflight, for navigation purposes. Based on the estimated state(s), themethod 200 can also generate instructions for flight control of theaircraft toward a flight path appropriate for the location of theaircraft, and can update flight control instructions as new data isreceived and processed. The method 200 can also include functionalityfor directly controlling flight of the aircraft at the location of theaircraft in a reliable and safe manner. The method 200 can beimplemented by one or more embodiments of the system 100 describedabove, in relation to FIGS. 1A and 1B. In particular, portions of themethod 200 can be implemented by the computing system componentsdescribed above, for instance, at portions of the computing systemoperating at a flight computer onboard the aircraft and/or portions ofthe computing system operating at a remote station with communication ofinputs and outputs across computing system components as defined by thearchitecture described above.

The method 200 thus functions to generate and process data from anon-traditional navigation system architecture to augment low altitudeflight operations (e.g., operations below a threshold altitude), inorder to generate better estimates of states of the aircraft in terms ofposition, movement, and orientation. The method 200 can also function togenerate and process data from a non-traditional navigation systemarchitecture to augment flight operations associated with other suitabletrigger, for instance, when position is uncertain but the aircraft iswithin range of radar communication apparatus. Generation of moreaccurate estimates of aircraft state, especially in low altitudeconditions, can improve navigation-based decision making (e.g.,automated decision making) and flight planning for the aircraft. Themethod involves implementation of radar tools to determine candidatelocations of an aircraft during flight, and augmenting data from othernavigation subsystems to hone in on a more precise location of theaircraft to assist navigation operations. The method also corrects fordrift in accuracy of navigation subsystems (e.g., of IMUs) and/or allowsnavigation subsystems to operate continuously when one or moresubsystems of the navigation subsystems are unavailable. For instance,the method 200 can provide accurate location identification even whenGPS signals are unavailable.

2.1 Method—Altitude Monitoring for Radar Receive Activation

As shown in FIGS. 2A and 2B, Blocks 210 a and 210 b includefunctionality for monitoring an altitude status of the aircraft duringflight of the aircraft. In particular, in relation to system elementsdescribed above, the flight computer 116 or other portion of thecomputing system (e.g., remote station 120, FMS 150) receives 210 a, 210b altitude measurements from an altitude sensor of an altimeter of theaircraft. The flight computer 116 or other portion of the computingsystem (e.g., remote station 120, FMS 150) can then optionally performan altitude status monitoring operation by processing the receivedaltitude measurements, and comparing the received altitude measurementsto a threshold condition. The threshold condition can be a thresholdaltitude of a set distance (e.g., 2000 ft., 2500 ft., 3000 ft., 3500ft., etc.) above ground level, a threshold altitude associated withlimitations of the radar subsystem in transmit/receive functions, athreshold altitude associated with computational ability to distinguishrelevant features from received radar signals, a threshold altitudeassociated with interference from other environmental aspects (e.g.,moisture in the air, particulate matter in the air, etc.), and/or anyother suitable threshold altitude condition. Outputs of the altitudestatus monitoring process include computer-readable objects indicativeof satisfaction of the threshold altitude condition by the measuredaltitude of the aircraft.

In some embodiments, the flight computer 116 or other portion of thecomputing system can omit adjusting navigation system states based uponaltitude thresholds. Still alternatively, in an embodiment where theradar subsystem 111 is articulated, the orientation of radar subsystem111 components can instead be adjusted between a first orientation(e.g., a forward orientation) to a second orientation (e.g., a downwardorientation) based on altitude of the aircraft 105 or another factor.

Based upon outputs of the altitude monitoring process, the flightcomputer 116 or other portion of the computing system (e.g., remotestation 120, FMS 150) transitions 220 a, 220 b a radar subsystem of thenavigation-related subsystems between an active mode for receiving radarsignal returns, and an inactive mode (e.g., whereby radar signal returnsare not received). In more detail, if an output of the altitude statusmonitoring process indicates that the measured altitude of the aircraftis above the threshold altitude condition, the IMU(s) and GPS componentsof the navigation-related subsystems are active and generate data thatis processed by the computing system (e.g., portion of the flightcomputer, portion of the remote station) to generate estimates of thestate of the aircraft (e.g., in terms of position, in terms oforientation, in terms of velocity, etc.). For instance, above thethreshold altitude, the computing system can directly process outputs ofthe GPS to extract position estimates (e.g., relative to geographiclocation) with coordinates and velocity estimates (e.g., in terms ofground speed, in terms of other aircraft velocities) and directlyprocess outputs of the IMU(s) to determine estimates of the orientationof the aircraft (e.g., in relation to directions of lateral motion, inrelation to directions of vertical motion in relation to rotation aboutpitch axes, in relation to rotation about roll axes, in relation torotation about yaw axes, etc.).

At or below the threshold altitude, the IMU(s) and GPS components of thenavigation-related subsystems are active and the radar subsystem of thenavigation-related subsystems of the aircraft 105 is active to receiveradar signals from objects associated with the flight path of theaircraft (e.g., objects below the aircraft). As such, at or below thethreshold altitude, the radar subsystem generates data that augmentsoutputs of the IMU(s) and the GPS to generate data that is processed bythe computing system (e.g., portion of the flight computer, portion ofthe remote station) to generate estimates of the state of the aircraft(e.g., in terms of position, in terms of orientation, in terms ofvelocity, etc.), according to downstream portions of the methoddescribed below.

2.2 Method—Generation of Candidate Aircraft Locations from Radar Signals

As shown in FIGS. 2A and 2B, when the aircraft is at or below thethreshold altitude, the computing system (e.g., portion of the flightcomputer, portion of the remote station, portion of the FMS) receivesradar return signals (e.g., radar signals reflected off of or scatteredfrom objects and back to receivers of the radar subsystems), andprocesses the radar return signals to determine 230 a, 230 b a heightestimate for one or more objects below or otherwise spatially relevantto flight of the aircraft. The computing system processes the returnedsignals transmitted toward a radar receiver ventrally-located at theaircraft to generate a height estimate, where the height estimate cancharacterize one or more of: a distance between the aircraft and theobject, an altitude at which the object rests (e.g., altitude aboveground level, altitude above mean sea level, etc.), a height of thetallest point of the object (e.g., in relation to ground level, inrelation to sea level), or any other suitable height-associated metric.In generating the height estimate, the computing system can determinedistances based upon time measurements between an emitted signal and areceived return signal corresponding to the emitted signal, with an echoanalysis including transit time components. Generation of the heightestimate can further incorporate aspects of signal wavelength, radarsignal pulse features, encoded signals within an emitted signal, and/orany other suitable component of the radar signal that can be used toestimate distances, and ultimately, a height of the object. However, asindicated above, the height estimate can additionally or alternativelybe determined through non-radar-based means (e.g., using LIDAR, usingstereocamera configurations, using monocular camera configurations,etc.). Furthermore, generating the height estimate can take into accountaircraft altitude and attitude aspects that can affect apparent altitudemeasured by radar analysis or through other means. For instance, thesystem can be configured to omit or adjust calculation of heightestimates when the aircraft is in non-straight and level flight (e.g.,during turns).

Additionally or alternatively, the computing system can determine otherfeatures of objects below or spatially relevant to a flight path of theaircraft. For instance, the computing system can determine objectcharacteristics including one or more of: object shape (e.g., uponprocessing multiple return signals that have interacted with differentsurfaces of the object), surface features of the object (e.g., basedupon analysis of radar scattering parameters, object speed (e.g., basedupon Doppler shift analysis), lateral distance to the object (e.g.,based upon transit time analysis of signals received from otherdirections), line-of-sight distance to the object, and/or any othersuitable object features to determine a location of the aircraft duringflight. For instance, radar reflectors positioned within observationrange of the navigation systems of the aircraft during flight can beused to improve reliability and/or accuracy of navigation functions.Appropriate positions of the radar reflectors can be determined basedupon surveying of terrain associated with flight operations, andmultiple radar reflectors distributed in a pattern can be used toprovide additional information or redundancy of radar reflectors.

As such, the objects include static objects positioned below orotherwise spatially relevant to a flight path of the aircraft. Staticobjects can include terrain, as shown in FIG. 2C, terrain features(e.g., bodies of land, bodies of water, waterways, geological features,etc.), natural objects (e.g., trees, boulders, fields), non-naturalobjects (e.g., buildings, transportation infrastructure, antennas,energy-harvesting structures, mines, other structures, man-made watermasses, etc.), and/or any other suitable static objects. Estimation ofaircraft location and/or state based on such static objects is describedin downstream portions of the method 200 below, and variations of themethod described below.

As shown in FIGS. 2A and 2B, the computing system (e.g., portion of theflight computer, portion of the remote station, portion of the FMS)receives the object height and/or other features of the object asdescribed above (e.g,. using radar, using LIDAR, using stereocamerainformation, using monocular camera information, etc.), and generates240 a, 240 b a set of candidate locations from the object height and/orother features. In one embodiment, the computing system compares theobject height to heights of objects in a database of navigation objectcharacteristics, where the heights of objects are surveyed at an earliertime during building of the database. The database of navigation objectcharacteristics thus includes heights of objects mapped to locations ofthe objects, such that object heights extractable from return radarsignals can be compared to entries in the database of navigation objectcharacteristics to identify height matches corresponding to objects, andthus candidate locations of the aircraft due to knowledge of the objectpositions corresponding to the object heights. The computing system in240 a, 240 b can additionally or alternatively use non-height-relatedfeatures of objects observable in the radar return signals, and comparesuch features against relevant database entries to generate the set ofcandidate locations. As such, the database can additionally oralternatively include object features mapped to location, where objectfeatures can be defined as described above.

2.3 Method—Determination of Aircraft Location and Updated State Estimate

As shown in FIGS. 2A and 2B, with the set of candidate locations outputfrom Blocks 240 a, 240 b, the computing system (e.g., portion of theflight computer, portion of the remote station, portion of the FMS)determines 250 a, 250 b the location of the aircraft upon processing theset of candidate locations with outputs of the IMU(s) and/or GPS, if GPSoutputs are available. The computing system thus selects the candidatelocation of the set of candidate locations that best aligns with the IMUoutputs and/or GPS outputs corresponding to the time stamp of thereturned radar signals used to generate the set of candidate locations.In one embodiment, the computing system compares coordinates of eachcandidate location of the set of candidate locations to GPS coordinatesextracted from the GPS output and determines the candidate location ofthe set of candidate locations that matches the location of the GPSoutput. In a related embodiment, if satellite signals to the GPS areunavailable at the time stamp associated with the radar return signalsused to generate the set of candidate locations, the computing systemcan determine an IMU-based location estimate from a reference output ofthe GPS (e.g., a GPS output of aircraft location when GPS signals werelast available) and position and velocity outputs of the IMU associatedwith the time stamp of the radar return signals used to generate the setof candidate locations. The computing system can thus facilitateIMU-enabled GPS operations, when satellite signals to the GPS areunavailable, to extrapolate location from IMU position and velocityoutputs and a reference location from the GPS. Then, the IMU-basedlocation estimate can be compared to coordinates of each candidatelocation of the set of candidate locations to determine the candidatelocation of the set of candidate locations that matches the location ofthe IMU-enabled output.

As shown in FIGS. 2A and 2B, the computing system also updates 260 a,260 b the estimate of the state (e.g., position in 3D space, velocity in3D space, and orientation in 3D space) of the aircraft based upon IMUand/or GPS outputs, and ties the state estimate to the location of theset of candidate locations that matches the available IMU and/or GPSoutputs. As such, a stream of state estimates of the aircraft arealigned with locations of the aircraft determined from radar-augmenteddata, in order to provide augmented and validated information toaircraft systems for navigation purposes.

2.4 Method—Improvement of State Estimates with Historical Indexing

As shown in FIG. 3A, the computing system (e.g., portion of the flightcomputer, portion of the remote station, portion of the FMS), incooperation with navigation-related subsystems, updates and maintains380 a running index of an aggregation of state estimates mapped to anaggregation of candidate locations and an aggregation of object heightsand/or other object features from historical flights of the aircraft. Assuch, during each flight and across different flights, the computingsystem generates index entries linking object heights (H), time stamps(t), candidate locations (locs), and state estimates (3D positions andorientations). The running index can then be used by the computingsystem to improve state estimate determination over time, as flightsover more locations are conducted and more entries to the running indexare generated. With aggregation of more radar-augmented flight data, thesearch space associated with the running index for each subsequentflight decreases.

In one embodiment 390 of use of the running index, as shown in FIG. 3B,for a subsequent flight, the computing system can determine a stateestimate and/or location of the aircraft in the subsequent flight basedon available entries of the running index. In more detail, the computingsystem processes returned radar signals to characterize 391 an objectheight ([Hx, tx]) of an object below the aircraft during the subsequentflight. The computing system can then perform a matching operation 392with the object height and the running index to determine a location andstate estimate of the aircraft that best matches the entries of therunning index. For instance, the computing system can take the objectheight, perform a search algorithm (e.g., index search algorithm, linearsearch algorithm, binary search algorithm, etc.) with the running indexto identify an appropriate entry of the running index, and identify thelocation and state estimate corresponding to the entry.

2.5 Method—Variations of State and Location Estimated with DifferentObject Types

The methods described above can be adapted to improve aircraft state andlocation estimation based on radar-detection of different types ofobjects spatially relevant to a flight path of the aircraft.

In one implementation as shown in FIG. 4A, navigation-related subsystems410 of the aircraft can generate 471 radar return signals from a staticobject (e.g., trees, fields, buildings, structures, etc.) below theaircraft (e.g., previously surveyed static objects to determine heightsof static objects for the height map database), and the computing system(e.g., portion of the flight computer, portion of the remote station)can process the radar return signals to generate 471 a height estimate(Hy) with a time stamp (ty) for the static object. The computing systemcan then process the height estimate against the running index and/ordatabase of navigation object characteristics described above, with aniterative solver operation 473 to output a location and state estimate(position in 3D space, orientation in 3D space, velocity, etc.) of theaircraft.

In one implementation as shown in FIG. 4A, navigation-related subsystems410 of the aircraft can generate 471 radar return signals from a staticobject (e.g., trees, fields, buildings, structures, etc.) below theaircraft, and the computing system (e.g., portion of the flightcomputer, portion of the remote station) can process the radar returnsignals to generate 471 a height estimate (H) with a time stamp (t) forthe static object. The computing system can then process the heightestimate against the running index and/or database of navigation objectcharacteristics described above, (e.g., with an iterative solveroperation 473 that gradually arrives at a solution while reducing theerror estimate in the solution) to output a location and state estimate(position in 3D space, orientation in 3D space, velocity, etc.) of theaircraft.

In another implementation as shown in FIG. 4B, navigation-relatedsubsystems 410 of the aircraft can generate 475 radar return signalsfrom an active radar-responsive object (e.g., marker) positioned belowthe aircraft, and the computing system (e.g., portion of the flightcomputer, portion of the remote station) can process the radar returnsignals with a marker feature analysis to generate 476 a location andstate estimate (position in 3D space, orientation in 3D space, velocity,etc.) of the aircraft. In more detail, as directed by computer controlof the radar subsystem, emitted radar signals (e.g., pulses, otherwaveforms) from transmit antennas of the radar subsystem can transition474 the radar-responsive mark into an activated mode, and the computingsystem can receive a response signal from the radar-responsive marker inthe activated mode. The response signal is then processed by thecomputing system to determine a location and state estimate of theaircraft. Information from the radar-responsive marker can alsosupplement height and feature-based analyses to generate a more preciseestimate of aircraft location with higher confidence.

In another implementation as shown in FIG. 4C, navigation-relatedsubsystems 410 of the aircraft can generate 471 radar return signalsfrom one or more moving objects (e.g., terrestrial vehicles, etc.) belowthe aircraft, and the computing system (e.g., portion of the flightcomputer, portion of the remote station) can process the radar returnsignals to generate 471 a derivative feature derived from a path ofmotion of the moving object(s). In more detail, the radar subsystem ofnavigation-related subsystems 410 of the aircraft can receive 477 radarsignal returns from the moving objects at multiple time points, wherethe radar signal returns are processed 478 by the computing system toextract height (H) and position (e.g., x, y, z position) of the movingobjects at multiple time points, with associated time stamps (t). Thecomputing system can then process the extracted height and informationdata to generate derivative features indicative of paths of motion ofthe moving objects. Derivative features can include morphologicalfeatures associated with the paths of motion, and in examples, includeone or more of: altitude changes in the path of motion, lateral positionchanges in the path of motion, shape features (e.g., radii of curvature,segment lengths, etc.) of the path of motion, boundaries of the path ofmotion along multiple axes, and any other suitable morphologicalfeatures. The computing system can then analyze the derivative featuresassociated with the path of motion to output a location and stateestimate (position in 3D space, orientation in 3D space, velocity, etc.)of the aircraft.

2.6 Method—Flight Control

As shown in FIGS. 2A and 2B, the method 200 can include functionalityfor controlling 270 a, 270 b flight of the aircraft toward a flight pathto the landing site. Based on the identified location and/or stateestimate, the computing system (e.g., a portion of the computing systemoperating at a flight computer onboard the aircraft, a portion of thecomputing system operating at the remote station, etc.) generatesinstructions for flight control of the aircraft as appropriate to thelocation of the aircraft. The flight computer or other computingcomponents controlling operation of flight control surfaces receive theinstructions and control operational configurations of one or morecontrol surfaces of the aircraft to maintain or redirect flight of theaircraft. As such, Blocks 270 a, 270 b include functionality forcontrolling flight of the aircraft toward the flight path upontransmitting the set of instructions to a flight computer of theaircraft and manipulating one or more flight control surfaces of theaircraft based on the set of instructions.

In Blocks 270 a, 270 b, the computing system (e.g., portion of theflight computer, portion of the remote station, portion of the FMS) canuse generated instructions to control configuration states of one ormore of: ailerons of the aircraft (e.g., to affect flight about a rollaxis), flaps of the aircraft (e.g., to affect rate of descent),elevators of the aircraft (e.g., to control flight about a pitch axis),rudders of the aircraft (e.g., to control flight about a yaw axis),spoilers of the aircraft (e.g., to control lift of the aircraft), slatsof the aircraft (e.g., to control angle of attack of the aircraft), airbrakes (e.g., to control drag of the aircraft), trim surfaces (e.g., tocontrol trim of the aircraft relative to any axis and/or reduce systemmechanical load), and any other suitable control surfaces of theaircraft.

In Blocks 270 a, 270 b, the computing system (e.g., portion of theflight computer, portion of the remote station, portion of the FMS)) canalso use generated instructions to control configuration states of powerplant components including one or more of: manifold pressure,revolutions (e.g., revolutions per minute), fuel mixture, electricaloutput from a battery, cooling system operational states (e.g., inrelation to cowl flaps, in relation to liquid cooling systems, inrelation to fins, etc.) for aircraft performance toward the landingsite.

In Blocks 270 a, 270 b, the computing system (e.g., portion of theflight computer, portion of the remote station, portion of the FMS) canalso use generated instructions to control other aircraft systemaspects. For instance, the generated instructions can be used to controlcommunications with air traffic control at the landing site, in relationto automated reception and/or read back of instructions from air trafficcontrol.

In relation to state of the aircraft (e.g., in position, in orientation,in velocity), the computing system generates instructions that accountfor aircraft orientation due to environmental effects. For instance, thecomputing system can generate instructions upon detecting crosswinds andcomputing a crosswind control factor for the ailerons and rudders of theaircraft. In another example, computing system can generate instructionsfor a flight path based on the location and prevailing winds at thealtitude of the aircraft.

In relation to state of the aircraft (e.g., in position, in orientation,in velocity), the computing system can also generate instructions thataccount for environmental effects due to terrain at the location of theaircraft. For instance, the computing system can generate instructionsfor increasing altitude over terrain associated with high winds, inorder to avoid turbulence . In another example, the computing system cangenerate instructions for control surface settings and/or power plantsettings based on aircraft location at a leeward/downwind side ofterrain, in order to avoid rotor effects.

However, the computing system can generate instructions used by theflight computer to control aircraft operation for other aircraftaspects, other environmental aspects, and/or other landing site aspects.

The method(s) described can, however, include any other suitable stepsor functionality for determining aircraft states while the aircraft isin flight, controlling flight operation of the aircraft, and/oraugmenting performance of navigation subsystems of the aircraft in anyother suitable manner.

3. Conclusion

The system and methods described can confer benefits and/ortechnological improvements, several of which are described herein. Forexample, the system and method employ non-traditional use of sensors(e.g., radar subsystems, IMUS, GPSs, etc.) to determine locations andstates of an aircraft while the aircraft is in flight at differentaltitudes. Navigation during flight, in particular, requires dynamicmonitoring and control of aircraft operational states, and the methodand system employ sensors in a novel manner for control of flight ofaircraft (e.g., fixed wing aircraft, other aircraft) as appropriate to aspecific location.

The system and method also reduces computing requirements and costsassociated with standard systems for navigation. For instance, by usingradar-augmented data and developing a database of locations and objectfeatures, the system is configured to ultimately achieve accuratedetermination of aircraft state and control of aircraft flight operationwith less computing power than other systems for navigation.

The system and method also include functionality for evaluatingperformance of other navigation subsystems of the aircraft (e.g., IMUsubsystems) to improve their performance, correct drift, or otherwiseimprove safety of a flight operation.

The system and method also include functionality for enablingdetermination of aircraft location and aircraft state during flight,even when other navigation subsystems of the aircraft (e.g., GPSsubsystems) are unavailable.

The foregoing description of the embodiments has been presented for thepurpose of illustration; it is not intended to be exhaustive or to limitthe patent rights to the precise forms disclosed. Persons skilled in therelevant art can appreciate that many modifications and variations arepossible in light of the above disclosure.

Some portions of this description describe the embodiments in terms ofalgorithms and symbolic representations of operations on information.These algorithmic descriptions and representations are commonly used bythose skilled in the data processing arts to convey the substance oftheir work effectively to others skilled in the art. These operations,while described functionally, computationally, or logically, areunderstood to be implemented by computer programs or equivalentelectrical circuits, microcode, or the like. Furthermore, it has alsoproven convenient at times, to refer to these arrangements of operationsas modules, without loss of generality. The described operations andtheir associated modules may be embodied in software, firmware,hardware, or any combinations thereof.

Any of the steps, operations, or processes described herein may beperformed or implemented with one or more hardware or software modules,alone or in combination with other devices. In one embodiment, asoftware module is implemented with a computer program productcomprising a computer-readable medium containing computer program code,which can be executed by a computer processor for performing any or allof the steps, operations, or processes described.

Embodiments may also relate to an apparatus for performing theoperations herein. This apparatus may be specially constructed for therequired purposes, and/or it may comprise a general-purpose computingdevice selectively activated or reconfigured by a computer programstored in the computer. Such a computer program may be stored in anon-transitory, tangible computer readable storage medium, or any typeof media suitable for storing electronic instructions, which may becoupled to a computer system bus. Furthermore, any computing systemsreferred to in the specification may include a single processor or maybe architectures employing multiple processor designs for increasedcomputing capability.

Embodiments may also relate to a product that is produced by a computingprocess described herein. Such a product may comprise informationresulting from a computing process, where the information is stored on anon-transitory, tangible computer readable storage medium and mayinclude any embodiment of a computer program product or other datacombination described herein.

Finally, the language used in the specification has been principallyselected for readability and instructional purposes, and it may not havebeen selected to delineate or circumscribe the patent rights. It istherefore intended that the scope of the patent rights be limited not bythis detailed description, but rather by any claims that issue on anapplication based hereon. Accordingly, the disclosure of the embodimentsis intended to be illustrative, but not limiting, of the scope of thepatent rights, one implementation of which is set forth in the followingclaims.

What is claimed is:
 1. A method for radar-augmented localization, the method comprising: with an altitude sensor, monitoring an altitude status of an aircraft in flight; in response to the altitude status satisfying a threshold altitude condition, transitioning a radar subsystem of the aircraft to a receive mode; from the radar subsystem in the receive mode, characterizing an object height of an object below the aircraft; generating a set of candidate locations of the aircraft from the object height; and determining a location and a state estimate of the aircraft upon processing the set of candidate locations.
 2. The method of claim 1, further comprising: upon detecting availability of a satellite signal from a global positioning system (GPS) of the aircraft, receiving a GPS output from the GPS and determining the location and the state of the aircraft from the set of candidate locations based on the GPS output.
 3. The method of claim 1, further comprising: with the state estimate, the set of candidate locations, and the object height, updating a running index of an aggregation of state estimates mapped to an aggregation of candidate locations and an aggregation of object heights from historical flights of the aircraft.
 4. The method of claim 3, further comprising: upon processing information from the radar subsystem in the receive mode, characterizing a second object height of a second object below the aircraft, performing a matching operation with the second object height and the running index, and determining a second location and a second state estimate of the aircraft from the matching operation.
 5. The method of claim 3, wherein the object comprises a static object positioned below the aircraft, and wherein determining the location of the aircraft further comprises applying an iterative solver operation to the object height of the static object and the running index.
 6. The method of claim 1, wherein the object comprises a radar-responsive marker positioned below the aircraft in flight and transitionable into an activated mode upon receiving a radar signal from the radar subsystem, the method further comprising emitting a radar pulse from the radar subsystem, receiving a response signal from the radar-responsive marker in the activated mode, and determining the location and the state estimate from the response signal.
 7. The method of claim 1, wherein the object comprises a dynamic object, and wherein the method further comprises determining the set of candidate locations from a path of motion of the dynamic object and the object height of the dynamic object.
 8. The method of claim 7, wherein the dynamic object comprises a terrestrial vehicle, and wherein determining the set of candidate locations further comprises receiving a set of radar signals returned from the terrestrial vehicle along the path of motion, and determining the set of candidate locations from the set of radar signals.
 9. The method of claim 1, wherein the object comprises a terrain feature positioned below the aircraft.
 10. The method of claim 1, further comprising: based upon at least one of the location and the state estimate, generating a set of instructions for a flight computer of the aircraft, the set of instructions for flight control of the aircraft toward a flight path appropriate for the location.
 11. A method for radar-augmented localization, the method comprising: with an altitude sensor, monitoring an altitude status of an aircraft in flight; in response to the altitude status satisfying a threshold altitude condition, transitioning a radar subsystem of the aircraft to a receive mode; from the radar system in the receive mode, characterizing an object height of an object below the aircraft; and determining a location and a state estimate of the aircraft from the object height.
 12. The method of claim 11, further comprising: receiving an inertial measurement unit (IMU) output of an IMU coupled to the aircraft and determining the location of the aircraft using the IMU output.
 13. The method of claim 11, further comprising: with the state estimate, the location, and the object height, updating a running index of an aggregation of state estimates mapped to an aggregation of candidate locations and an aggregation of object heights from historical flights of the aircraft.
 14. The method of claim 11, wherein determining the location and the state estimate comprises applying an iterative solver operation to the object height and a running index of an aggregation of state estimates mapped to an aggregation of candidate locations and an aggregation of object heights from historical flights of the aircraft.
 15. The method of claim 11, further comprising: based upon at least one of the location and the state estimate, generating a set of instructions for a flight computer of the aircraft, the set of instructions for flight control of the aircraft toward a flight path appropriate for the location.
 16. A system for radar-augmented localization, the system comprising: a navigation subsystem coupled to an aircraft and comprising a radar subsystem oriented to receive radar signals transmitted toward a ventral portion of the aircraft; a data transmission subsystem in communication with the navigation subsystem; and a computing system in communication with the data transmission system and comprising machine-readable instructions in non-transitory media for: monitoring an altitude status of an aircraft in flight; in response to the altitude status satisfying a threshold altitude condition, transitioning the radar subsystem of the aircraft to a receive mode; from the radar system in the receive mode, characterizing an object height of an object below the aircraft; generating a set of candidate locations of the aircraft from the object height; and determining a location and a state estimate of the aircraft from the object height.
 17. The system of claim 16, wherein the navigation subsystem further comprises an inertial measurement unit (IMU) mounted to the aircraft, and a global positioning system (GPS) coupled to the aircraft, the IMU and the GPS communicatively coupled to the computing system and the radar subsystem.
 18. The system of claim 17, wherein the computing system further comprises instructions for determining the location of the aircraft from processing the set of candidate locations with an IMU output of the IMU and a GPS output of the GPS.
 19. The system of claim 16, wherein the state estimate comprises a position, a velocity, and an orientation of the aircraft.
 20. The system of claim 16, further comprising an electronic interface between the computing system and a flight management system of the aircraft, the electronic interface operable in a mode that transmits the set of instructions to the flight management system and controls flight of the aircraft toward the flight path. 